Wet Torrefaction of Poultry Litter in a Pilot Unit: A Numerical Assessment of the Process Parameters

Torrefaction of walnut oil processing wastes by superheated steam: Effects on products characteristics

Walnut oil production waste (WOPW) is a by-product of walnut oil processing. The organic waste is rich in holocellulose and lignin, showing good potential to be converted by thermal process to valuable products. Superheated steam (SHS) torrefaction is a recently proposed thermal process enabling fast and unformal biomass heating, resulting in high-quality solid products as direct fuel. The potential of SHS to torrefy lipids and proteins (being rich in WOPW) is attractive for broader application of SHS torrefaction to upgrade more biomass wastes. SHS torrefaction was studied in this work to upgrade WOPW for solid products with different reaction temperatures (200, 250, 300 °C) and residence times (20, 40, 60 min). The lowest weight yield was 43.64 wt% under the severest treatment of 300 °C and 60 min, accompanied with the highest energy enhancement of 1.34 (reaching HHV of 27.03 MJ/kg). Response surface method is employed to reveal the effects of temperature and residence time. Residence time of 40 min under 300 °C was supposed to be an ideal condition to upgrade WOPW with HHV of 26.68 MJ/kg and in the range of coal from Van Krevelen diagram. Combustion indices (e.g., fuel ratio, combustion index, and volatile ignitability) indicated that the aforementioned torrefied WOPW had favourable properties as co-firing material. On the other hand, combustion behaviours analysis demonstrated that SHS torrefied WOPW could perform well as direct fuel. Aqueous effluent was also condensed and analyzed, where products from lipids and proteins were massively presented, giving an insight into the decomposition of those two constitutes undergoing SHS torrefaction.

Some Results of Poultry Litter Processing into a Fertilizer by the Wet Torrefaction Method in a Fluidized Bed

Poultry litter mass is formed in large quantities at poultry farms producing poultry meat (1–3 kg of litter mass per 1 kg of produced meat). These wastes represent a threat to the environment because of the presence of pathogenic microflora in them and the greenhouse gas emitted during the storage of these wastes. The procedure of poultry litter mass processing by wet torrefaction in a superheated water vapor environment at a temperature of 150–260 °C is studied. It is shown that after torrefaction at a temperature of 150 °C, the poultry litter mass retains high humidity, i.e., it represents an environment suitable for the re-development of pathogenic microflora. Only after wet torrefaction at a temperature of 260 °C does the humidity of the poultry litter mass decreases to 4%, and the risk of re-infection with pathogenic microflora decreases sharply. The absence of nitrates in the samples after torrefaction at a temperature of 260 °C indicates the termination of the activity of nitrifying bacteria. After torrefaction at a temperature of 260 °C, the poultry litter mass has a pH close to 7. This increases the mobility and availability of microelements for plants. Torrefaction at a temperature of 260 °C increases the content of ash, phosphorus and potassium by 30–40% and nitrogen by 15–20%, which makes the fertilizer more concentrated and optimizes the ratio of nitrogen, phosphorus and potassium. After wet torrefaction, due to the burning of the most easily degradable nitrogen-containing organic compounds and the destruction of some organophosphorus compounds, the mobility of nitrogen decreases, and the mobility of phosphorus increases. As a result of the research, it was found that the treatment of poultry manure by wet torrefaction in an environment of superheated water vapor at a temperature not lower than 260 °C makes it possible to obtain organic fertilizer with the most optimal nutrient content.

Characteristics of Hydrochar and Liquid Products Obtained by Hydrothermal Carbonization and Wet Torrefaction of Poultry Litter in Mixture with Wood Sawdust

Poultry farms with floor-standing poultry generate large amounts of poultry litter waste. The direct application of this waste as an organic fertilizer does not ensure sustainable and cost-efficient utilization of all waste fractions, and can also be linked to environmental hazards. Therefore, the development of new technologies is required for processing poultry litter into a safe product with higher added value. In this work, the characteristics of activated carbon derived from hydrochar, along with the liquid products obtained from hydrothermal carbonization (HTC) and the wet torrefaction (WT) of poultry litter, were investigated. Poultry litter (PL) was applied in a mixture with sawdust (SD) in the following ratios: 1:0 (PL/SD 1:0), 1:1 (PL/SD 1:1), 1:2 (PL/SD 1:2), and 2:1 (PL/SD 2:1). WT processing took place in an innovative fluidized bed system in a superheated steam medium with low overpressure (less than 0.07 MPa) at 300 °C and 350 °C for 30–45 min. Conventional HTC processing was performed in a water medium at 220 °C for 1–4 h. The hydrochar produced in the experiments was activated with steam for 1 h at 450–750 °C. The porosity characteristics of activated hydrochar were measured, including pore size, pore volume, and specific surface area, in view of potential industrial applications as an adsorbent. Additionally, the contents of 5-hydroxymethylfurfural (HMF), as high-value product, were determined in the liquid products obtained from HTC processing, as well as in the condensate obtained after WT processing. Specific surface areas of the activated hydrochars may still be too low for application as adsorbent material. Hence, its use as a biofertilizer and soil improver should be preferred. Interestingly, the liquid fraction obtained from the innovative WT process displayed a significantly higher 5-HMF content compared to the conventional HTC process.